1. Field of the Invention
The invention relates in general to a manufacturing method of a multi-layer circuit board, and more particularly to a manufacturing method of a multi-layer circuit board embedded with a passive component.
2. Description of the Related Art
The object of creating a larger space within a substrate area with limited space and enhancing the multi-functions of the module is normally achieved by reducing or embedding a passive component so that more space can be used for the installation of active components. And, the multi-layer circuit board embedded with a passive component is thus invented and provided. The above passive component can be components such as a resistor, a capacitor, an inductometer or a voltage controlled quartz oscillator.
Many methods can be used to integrate several film passive components in a multi-layer circuit board. In terms of the manufacturing process of multi-layer circuit board, the key factor lies in the ability of embedding the thick-film or thin film passive component of the kind in the circuit board during manufacturing process. The key factor is how to maintain the electrical precision of the thin film passive component and reduce the variation with the original design after the thin film passive component is integrated into the multi-layer circuit board. An exemplified in Taiwanese Patent Publication No. 518616 “Manufacturing Method of a Multi-Layer Circuit Board with a Passive Component” disclosed on Jan. 21, 2003 is an example focusing on this issue.
Referring to FIG. 1A and FIG. 1B, a multi-layer circuit board with a passive component includes a circuit thin plate 1 whose surface has a patterned circuit layer 2, a conductive foil 3, a resistor film 5, a passivation layer 7, and a prepreg 9. The resistor film 5 is deposited on a slightly rough region on a smooth surface of the conductive foil 3 to have a better adhesion, and can be appropriately heated to become solidification. The slightly rough region can be defined according to photoresist micro-film etching, polishing, or other methods. The passivation layer 7 covers up the resistor film 5. The prepreg 9 is located between the conductive foil 3 and the circuit thin plate 1. The circuit thin plate 1, the conductive foil 3, and the prepreg 9 are stacked together according to a hot-pressing step.
However, the above methods must take into account the manufacturing process ability of the resistor or capacitor. For example, the printing area of the resistor must be carefully controlled, lest the printed resistor might vary with the designed value and cause bias to electrical precision. Therefore, the entire manufacturing process would become more complicated.
In the fields of close-to-mature technology, how to maintain the electrical precision and at the same time simplify the manufacturing process for the current manufacturing process to better fit the needs of next generation products has become an urgent issue to be resolved.